Guys,

Just finished my 9mm build and am having an issue with failures to fire.

9mm TROS barrel
RRA Bolt (ramped)
DPMS style hammer.

I am getting some failures to fire by way of the firing pin not striking the primer hard enough. The rifle is chambering the rounds but when I get a failure to fire, I can see a very light strike on the primer surface.
This is only happening about 2 out of 10 rounds. But it is ANNOYING.

I understand that this platform is an inertia type firing pin and that it must be sent forward hard enough to dent the primer cup. That the firing pin will not come to rest against the primer with the weight of the hammer behind it. So I don't know what to do.

Any ideas?

You may have a weak hammer spring or the firing pin is not traveling forward
enough to dent the primer.
clean your bolt inside where the firing pin is for a start, maybe some dirt or debreeee
in there.

Are you sure you feel the hammer fall on the failures. It may also be that the hammer isn't setting and rides the bolt home and causes a light strike. This is usually symptomed by a double now and again so it may not be this issue.

Yep, I agree with the above.  Check for Hammer bouncing off of the sear and riding the bolt forward.  9mm is especially nasty and with a can it's even worse.  Try cleaning then replace with a heavier buffer.  My 9mm did not work even with a Hahn 9oz bolt.  so had to make one 11.5oz so it would work with the suppressor.  my 2 cents

I had a similar experience when I first got my 9mm.  I removed the firing pin spring and clipped a couple of coils off.  Has run like a champ ever since.

YMMV

ETA:  Like others suggested above, look into a heavier buffer.  I use an Endine and it's great.

Yes. The hammer is in fact being cocked. The problem is that when the hammer strikes the firing pin (even if I re-cock it and go thru multiple attempts at firing again) it is not striking the primer to fire the round.

Then, when it decides it wants to work again, it will run like a sewing machine for several rounds. And when I change mags or set the rifle down for a moment, then go to fire again....CLICK.

Silly musings, but here they are anyway:

Chamber cut properly to spec?
Ammo in spec - factory or reloads - too large for chamber - high primers on some?
Upper/bolt assembly in spec and put together properly?  Nothing preventing the bolt from closing fully on every chambered round?
Damaged/broken firing pin?  Have a known good one you can check it against?

Good luck!

TROS barrel. To spec as far as I can tell. The problem only happens about every 1 in 20 rounds.

Ammo is factory Winchester 115 grn. Not reloads.

Upper and bolt are properly assembled. Bolt is factory RRA, so is upper.

Firing pin is also brand spanking new.

If your hammer spring and firing pin spring check out as mentioned above, the only other thing I can think of is something in the firing pin channel might be causing the pin to get hung up.

You can remove your bolt, disassemble it, and check that the firing pin moves freely in the channel.

It has also happened that sometimes when these rounds fail to fire, they also do not extract manually. It is as if the extractor is not grabbing a firm hold of the rim of the case. But not always. I had already disassembled the bolt and checked the firing pin and so forth. All seemed fine.

Since the bolt has a 1911 style extractor, is it feasible that I might need to bend the extractor inward toward the center slightly?

I fired the rifle again today. It would fire 20 rounds in a row no problem. But then again, when it decided to not fire, it would do that thru 3-5 rounds, having to manual eject them...then when it decided to work, it would work flawlessly. I am at a loss.

This may be grabbing for straws but it's worth a quick check.
Make sure your hammer spring is installed correctly.
If it's installed backwards it will still work but will hit with very little force.
I have actually seen this before. OK, I did it before.

It's in correctly.

Pull your barrel and use a live round as your test device.. drop the round into the chamber, and measure the amount of case sticking out of the end of the barrel.

Ideally the minimum should be .125", NO LESS.    I like to see .130 to .135" from of case out the end of the barrel.  Measure the bolt face depth, and common depth is .125".

With the std bolt depth of .125, and combine this with the .130" out the end of the barrel, you be rest assured that the case is firmly supported by case mouth and bolt face, thus the fire pin will strike the primer firmly.

Also, this will keep the bolt face from slapping the end of the barrel, and only rest on barrel when action is closed on empty chamber.

I had somebody make a stainless barrel a little over 5yr ago, and had to unscrew their
headspacing mistake via facing off end of barrel and setting the barrel back in the upper to synchronize the end of bolt with upper receiver when bolt closed.


In the pic, you can see where I had to cut the flange to set the barrel back (see gap between flange and index pin) after facing off the end of barrel to get the protrusion I wanted...  Had to do same with recent barrel purchase from another vendor to correct the headspacing to my specs.

SBR7_11, You were right. The chamber was out of spec. I contacted TROS and Mark is having me send it back to him for a free replacement. The chamber was machined too deep and it was allowing the bolt to rest on the barrel, preventing the base of the cartridge from contacting the face of the bolt. That is why the firing pin could  not always contact the primer.

It would only contact the primer if the case somehow ended up under the extractor during chambering, in which case it would fire with too much head space. Bad joojoo.

that is bullshit.  I sure hope they give you some free stuff for your frustration.

Thats what I thought, as with mine I took the extractor out, and set a round in the chamber (this is with the upper removed from the lower), then closed the bolt and held, I could see substanitial gap betweem case and bolt face, and the round could be freely moved fore-aft  (case not firmly supported between case mouth and base).

Anyway, make sure Mark sets you up with what I prefer to be a .130 - .135" case protrusion, and you may find your suppressor use to be a lot quieter experience.


EDIT: poor spelling skills at times....

BTT

Any word on the replacement barrel ?

BTT for another fella with problems